Amazon is seeking up to 1 million square feet in Boston

The Fan Pier and Seaport in Boston. David L. Ryan/Globe Staff

Amazon is on the hunt for as much as 1 million square feet of office space in Boston, adding a new level of intrigue to the retail giant’s plans as it whittles down the list of the cities competing for its second headquarters.

The Seattle company is negotiating with a Seaport developer to lease an entire office building, and possibly two, to continue its expansion in the city, according to real estate industry executives with knowledge of the talks.

Amazon employs more than 1,000 people in Boston and Cambridge — mostly software engineers and developers — with offices open or under construction in Kendall Square, the Back Bay, and Fort Point. It expects to nearly double that number over the next few years, and could grow even larger here with more space in the Seaport.